It is known to provide metallic gaskets for sealing opposed joint surfaces of a cylinder head and a cylinder block of an engine. Typical gaskets are provided with apertures which cooperate with the combustion chambers, water passages and oil passages in the engine. The apertures are further provided with some kind of sealing element.
Known sealing elements have included a separate sealing layer for the gasket, a welded on shim, or a thermal spray deposit applied to the outer surface of the gasket. Sealing elements of these types involve more materials, more assembly time, and therefore disadvantageously increase production costs.
Other known metallic gaskets include a metal plate having a substantially uniform thickness that has a portion near the apertures folded over onto the metal plate to create an increased thickness sealing surface. Such sealing elements often exhibit performance problems as the fold areas are prone to cracking due to the thickness of the metal plate.
To overcome such problems, one known gasket includes a metal plate that is provided with stepped portions such that the thickness of the plate is varied. The metal plate is folded at the portion of the plate that has a reduced cross-sectional thickness than the remainder of the plate. However, providing the stepped portions on the plate involves an extra machining step, as well as a specialized tooling set up to achieve precise tolerances, thereby serving to drive production costs upward.
Other known gaskets that have folded sealing elements utilize a metal plate with a substantially uniform thickness, but which further includes the addition of annular grooves in a surface of the metal plate. The grooves are positioned at the fold line and at that part at which the free ends of the folded portions are positioned such that the folded free ends do not come into contact with the metal plate. Gaskets of this kind also involve a separate expensive machining step to form the annular rings, thus increasing production costs.
Another known gasket only incorporates sealing beads as the sealing element on the perimeter of the gasket aperture. Sealing beads alone are unsatisfactory because significant compression is necessary to cause the beads to bear against the flanges of the cylinder head and cylinder block to create an adequate seal.
Therefore, there exists a need for a gasket having a minimum number of parts that can be manufactured cost-efficiently without sacrificing sealing effectiveness.